Gaslighting and disagreeing are two different things. Gaslighting is phony and unaccountable. It's playing a game of optics, saying something you don't actually believe in order to manipulate perceptions and suppress a true story. Disagreeing is simply countering because you genuinely believe otherwise. But there is some overlap when the disagreeing is unaccountable. In other words, you disagree, but you won't hear or consider or adapt to new information: that's the root of delusionality.

Now, sometimes a person does hear new information (or they actually heard it or thought it before), but they don't do a good job of making it clear, out loud, that they heard it. This is very common in discussions, but it's also very common that people simply brush information aside intentionally. One way they do the latter is by mockery, shaming, etc. They use emotional tactics to distract from the information they don't know how to respond to. This too is a root of delusionality. But they may actually believe they are arguing well, so in that sense they are not being phony or intentionally manipulative.

What I'm saying is that when you are not accountable in your reasoning - or even just when you aren't clear enough about what you have heard and understood from another person - it can come across as gaslighting, even though it's either garden variety delusionality (groupthink, lack of critical thinking, other biases) or failure to repeat back what's heard.

It's very common for someone to hear a line of argument, say basically nothing about it (or else throw in some words of mockery), and then provide a completely different line of argument to try to one-up the first.

One of the quickest ways to seem illogical - and become illogical - is to ignore other people's reasoning. If you aren't actually addressing someone's argument directly, you very likely are not one-upping it.

In a debate there is an unspoken expectation that you actually respond to what others say, that you don't just ignore it when it's convenient to ignore it. Anyone of course is free not to meet that expectation, but they should be aware that a tendency to ignore others' points strikes some people as very far from subtle and as an indication of incompetence.

I don't trust what someone says because they say it firmly. I trust what they say because they can handle disagreement and respond to it directly without cheap tactics like shaming, ridicule, etc (I'd make an exception for comedians or moments of comic relief, but laughing at a thought, or getting others to laugh at it, is extremely far from a reliable way to address it).

If you show off that your thought process is unreliable in its core strategy, then you give me less reason to trust what you say.

If you show off that your thought process is scrupulously accountable, then you give me reason to trust what you say.

It has nothing to do with how bold or certain someone sounds. And it isn't about gaslighting or not gaslighting, usually - though the former certainly puts someone in the "unreliable thought process" category.